The BP Amoco Polymers facility off Tobacco Road released the findings of the company's internal investigation Friday - the four-month anniversary of the fatal blast.

The reaction inside the waste collection drum, or knockout pot, came during an aborted start-up of the Amodel unit, the company says. Polymers foamed and coated the inside of the drum. Pressure built up. The knockout pot's lid blew off when workers removed bolts to open it for cleaning.

In the same manner as the report by the Georgia Department of Labor, the plant's findings steer away from a defective gauge on the dump tank. The families of two victims - Henrich Kohl, 25, and John Rowland, 35 - have filed a wrongful death lawsuit against Modern Welding Co. of Kentucky, Modern Welding Co. of Georgia and Dresser Industries, the makers of the vessel and its gauge.

George Sanders, 42, also died in the blast.

The tank had been filled with hot polymer waste. The chemical reaction made materials inside the tank like an "M&M candy" - an outer shell crystallized while waste continued brewing inside, BP Amoco Polymers spokeswoman Pam Barbara said.

Because of the outer shell, the vessel's gauge did not give an accurate reading. The employees began removing the cover plate - the gauge registering that the tank had been depressurized - just before their deaths.

Attorneys for the Kohl and Rowland families could not be reached for comment Friday.

Atlanta attorney Charles R. Beans, who represents Modern Welding, the vessel's manufacturer, said he expects his client to be exonerated. The vessel worked properly in its function at the plant, he said. It was being used to collect waste in the production of Amodel, a heat-resistant plastic used in car parts.

"Everything we've seen from the beginning, including this and the Department of Labor's report, definitely points away from us and agrees with our conclusions," Mr. Beans said.

The Labor Department's report says sign-out sheets documenting the employees' shutdown procedures to isolate the tank had not been completely filled out. Ms. Barbara said plant officials believe the explosion would have occurred whether or not proper shutdown procedures had been followed.

The company is unaware of any similar mishaps occurring at other plants, Ms. Barbara said. The federal Occupational Safety and Health Administration and the U.S. Chemical Safety and Hazard Investigation Board are still looking into the explosion.

The plant's Amodel unit will be restarted the week of July 23, Ms. Barbara said. Knockout pots will no longer be used. Instead, polymer waste will be channeled through a system that mixes it with water for cooling, grinds the mixture, then funnels it into drums for disposal.

Employees will no longer need to open waste tanks when the unit is shut down, Ms. Barbara said.